Large-current ion implantation apparatus performs ion implantation with an ion beam having a large current value in order to introduce a number of ions per unit time into a substrate. For this reason, the substrate itself is gradually charged up during execution of the ion implantation. If this charge build-up results in discharge, the substrate can be damaged by the discharge. In order to avoid such an accident, a charge neutralizer is used to prevent the charge build-up on the substrate. The charge neutralizer generates electrons for relieving the damage due to the charge of the substrate, whereby the negative charge of the electrons neutralizes the positive charge of ions to be implanted.